Process for preparing a polyfluoro alkanol



PROCESS FOR PREPARIN A POLYFLUORO ALKAN Viktor Weinmayr, Landenberg, Pa., assignor to E. I. du .Pont de Nemours and Company, Wilmington, Del., a ""co oration of Delaware v N o Drawing. Filed May 20, 1959, Ser. No. 814,386

' i 6 Claims. ((11. 260-33),

This invention relatesto a novel process for preparing 1H, 1H-2- (trifluoromethyl) -tetrafluoro-1 -propanol.

having the formula CFa-QF-CHzOH is a member of a class of alcohols which are well known compounds that are valuable for many purposes, partic-- ularly as intermediates for the preparation of other comincluding polymerizable esters, derivatives having low surface tension, dyes, insecticides and medicmals.

- v The methods heretofore used for the preparation'of polyfluoroalkanols are complex and hazardous and re- -quire high-cost starting materials. For example, polyfluoroalkanols have been made by reducing perfluoroalkanecarboxylic acids with lithium aluminum hydnde as disclosed by Husted et al. in J.A.C.S. 74, 5422 (1955) and from perfluoro aliphatic aldehydes by reaction with to provide such a process which can be readily carried out, which employs readily available starting materials, and produces the desired product in high yield and high purity, and which can be practiced on a large scale without undue hazards. Other objects are to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished in accordance with this invention which comprises reacting about 0.5 mole of hexafluoropropylene with '1 mole formaldehyde, which may be in polymeric form, and at least 2 moles of hydrogen fluoride at a temperature in the range of from 100 C-tO 200 C. and a pressure in the range of from about 600 p.s.i.g, to about 2500 p.s.i.g., there being present notmore than 1 part of water for each part of hydrogen fluoride, and separating from United States Patent V O '20 pounds containing a polyfluoro alkyl group such as esters,

the reaction mass lH,lH-2-(trifluoromethyl)-tetrafluorol-propanol.

The process of this invention is simple and readily carried out in conventional reaction vessels that may be heated and agitated and which will withstand the pressures encountered in the reaction. The reaction vessel will be constructed of or lined with a material or materials that is resistant to the corrosive action of anhydrous hydrogen fluoride and/or concentrated solutions of hydrofluoric acid. suitable materials of construction'include platinum, silver, nickel, stainless steel and Hastelloy.

The process may be carried out as a batch process with the intermittent addition of hexafluoropropylene to a solution of formaldehyde or of a polymer thereof in hydrogen fluoride or with the intermittent addition of a solution of the formaldehyde or of its polymer in hyl atented Sept. 12, 196.1

ice

In a batch or intermittent process, the manner inwhich the hexafluoropropylene is brought into contact with the formaldehyde solution in hydrogen fluoride may be varied widely Without significantly changing the over-all results. The reaction may be run under a constanthexafluoropropylene pressure, the amount of hexafluoropropylene to be employed may be charged in a single batch to the reaction vessel at the start of the operation, or hexafluoropropylene may be added intermittently, allowing the pressure to drop after each addition thereof, until no decrease in pressure witha subsequent addition of hexafluoropropylene indicates thatthereaction is complete. The presently preferred process comprises heating a 20% to 25% solution of paraformaldehyde in anhydrous hydrogen fluoride to C, to C. and, at thigtemperature with constant agitation, maintaining a pressure of about 2000 p.s.i.g. to about 2100 p.s.i.g. with-hexafluoropropylene for 2 to 24 hours.

The lH,lH-2-(trifiuoromethyl)-tetra fluoro-l-propanol may be isolated from the reaction mass in a number of Ways which are described hereinafter in some detail.

Atmospheric oxygen tends to initiate self-polymerization of the hexafluoropropylene. To prevent the p0ssibility of such self-polymerization, the reaction usually should be carried out in the substantial absence of air. Therefore, the equipment should be carefully flushed with an inert gas, such as nitrogen, to remove air as. far as practicable before the introduction of any reactant which is volatile at the temperature of the reaction vessel. For example, when paraformaldehyde is used, it may'be charged to the vessel before the vessel is flushed with the -When other polyfluoroolefins, such as hexafluorocyclobutene, perfluoroisobutylene, the dimer of hexafluoropropylene, the trimer of hexafluoropropylene, and 9H- polyfluoro-l-nonene, were employed in the place of hexafiuoropropylene in the process of this invention, the expected polyfluoroalkanols could not be identified in the reaction mass. Tetrafluoroethylene requires different critical conditions and the process as applied thereto is disclosed and claimed in my copending application, No. 814,415, filed May 20, 1959.

The hexafluoropropylene employed in this process may or may: not contain a polymerization inhibitor. Usually it is preferred to employ the commercially available hexafluoropropylene which contains a polymerization inhibitor so as to ensure against any possible polymerization of the hexafluoropropylene. The presence of the polymerization inhibitor does not affect the reactivity of the hexafluoropropylene in this process or afiectthe yield or quality of the desired products;

The formaldehyde may be used in its unpolymerized Serial form or in the'form of one of its polymers, such as. tri- "oxaneand paraforrnaldehyde, without infecting the rate or the course of the reaction. For ease ofhandling and forveconomic reasons,the formaldehyde ordinarily will beinfiiheform of parafornialdchyde. Otheraldehydes, *slibh' ascetaldhyde, paraldehyde (a 'polymeridform of aee araehyae) and benzaldehyde' were'found to be inopera'ble 'inthe process of this invention. 7

Preferably, the hydrogen fluoride will "be anhydrous hydrogen-fluoride; 'This is for practical reasons, such as keeping the corrosion of the equipment at'a minimum. It

cessive decrease'in the yield of the desired product.

,fI'heianhydroushydrogcn' fluoride need not be completely Isponding decrease in the production of the desired prod "ucts firom a given amount offormaldehyde, and more thanthis amount comprises an excess of hexafluoropropylene which must be recovered or will be wasted.

Although the stoichiometric'equation for the reaction of this process requires only 1 mole of hydrogen'fluoride for eachmo'le of formaldehyde, it has'been found that at least '2rnoles ofhydrogen fluoridefor each mole of "tormaldehydernnstbe' used. Materially smaller proportio'ns of hy'drogenfluoride fail'to produce the desired r'eaction-andiproduct. Usually, there will beemployed from'about 3 to about 7frno1es of hydrogen fluoride for "each'mole of formaldehyde,'preferably 4-to 5 moles'of hydro'genfluoride. Much larger excesses of hydrogen "fluoride may be used, but such'excesses provide no advantageandmerely' increase the problem of recovering the excesshydrogen'fluoride. f

The" excess hydrogen'fiuoride' andthe lI-LlH-Z-(trifluo'rornethyl) -tetrafluoro-l-propanol "may .be separated isnnnecessar toeniploy specialprecautions to maintain anhydrous conditions-for the" reaction to. proceed 'satisv ifacforifi; Aqueous'hydro fluoric acid of 50% concentra- V Itionor higher' may befused. More dilutehydrofluoric acid tends to cause'exccssive corrosion-of'the equipment 7 reaction Imass after the hexafluoropropylene/formaldehyde/ hydrogen 'fluoride reaction has taken place, with the same eifect of producing a cleaner separation of the hydrogen fluoride and the alcohol during the distillation, yielding the alcohol substantially free of hydrogen fluoride. However; in thelatter ease; the sulfuricracid should be in a proportion of at least-% by weight of the reaction mixture treated, usually from about 20% -*to a'hout 50%-and preferably-from about to -about 40%.

The reaction may be carried out at a temperature'in the range of frorn 100 C. to 200C. For a smooth, controlled reaction with high conversion and yield, the temperatures usually will be in the range of from about 125 C. to about 165 C., preferably from about 155 C. to about 165 C. 'As-the temperatures are increased above 200 C. there is an 'incrca'sdtendency for'the formation of undesirable by-products whichcause' a corresponding reduction intheyield 0f the desired product. The pressure usually will depend partly upon the amount of hexafluoropropylene charged to the reaction vessel and present at any givenstageof lthe'reac'tion and partly upon the temperatureat whichthe reaction is'ruu.

"The pressure niayrange from about 60O p.s.i.g. (pounds from the reaction mass by fractional distillation or by dilution with ice and neutralization followed by distillation. 1f it is desired to obtain directly from the reaction mass "a clean separation of hydrogen fluoride and substan tia lly pure 1H,1H2-(trifiuoromethyl) tetrafluoro-l-propanol'by a'fractional distillation, the reaction may be carried out in the presence of concentrated "sulfuric acid or, preferably, concentrated sulfuridacid'wilfbe added after the reaction has taken place, followed "by fractional dis- "t'illation of the mixture.

lithe-reaction is carried out in the presence of concenarmed sulfuric acid, the-acid used should beof about "96%to100% concentratiomemploying at least about 5% -by'-wei'ght ofthe concentratedacid based on'the'total weight of the other reactants. Usually, the concentrated sulfuric acidwill-be present in the proportion of from' about 20% to about 50% by weight and preferably from -about' 20"'%v to about' 3O%"by weight. -The concentrated *sulfuric acid has the advantage that, when the reaction "mass is fractionally distilled, the excess 7 hydrogen fluoride, insubstantial-1ypureanhydrous' form, and essentially'pure anhydrous 1H,1H-2'(trifluoromethyl) -tet'raflnoro-1-prop-a- $01, substantially free from hydrogen fluoride, are readily obtained as separate fractions. ime-concentrated sulfuric acid may 'be' adde d to the per square inch gauge), to about 2500"p'.s.i .g. Usually,

the pressure'will be the autogenous pressure at therein- .perature employed. At temperatures in the-range of from "about 125 C. to about 165 C. 'the preferred pressure is from about 925' p.s.i.g.*to about 210O p.s.i.g. The "pressures can be independently increased funther-by compression or by introduction of thehexafluoropropylene or 'otan inert gas such as nitrogen under the desired pressure. With little orno excess of hexafluoropropylene over the' 'stoi'chiometric amount, the pressure "decreases during the reaction 'as the hexafluoropropylene is consumed.

In orderto more clearly illustrate this invention,- presently preferred modes of carrying it -into effect and "advantageous results obtained, the following examples are given in which the'proportions are by weight except where specifically indicated-otherwise.

Example 1 monia Tgas. Upon steam"distillation, 28 parts ofa-waterinsoluble material formed as-a' lower layer'in the distil- "late. This product was fractionated, distflling at-94.5 C.,

and identified by infrared analysis and nuclear magnetic resonanceas 1H,1H-2-(trifluoromethyl)-tetrafiuoro-lepropanol.

Example) By the procedure of Example 1, 60 g. of paraformaldehyde, 200. g. of hydrogen fluoride, and g." of hexafluoropropylene were heatedfor8 hours at 160 C. The

maximum recorded pressure was 2100 p.s.i.g. Twenty grams ofsteam distilled,'unrefined 1H',1H-'2'-(trifluoromethyl)-tetrafluoro-l-propanol were obtained;

I Example 3 'The samecharge or reactants used in- EXampleZ was heated for 12'hours'at 125 C. The maximum recorded pressure was 925 p.s.i.g., and the yield of unrefined 1H, 1H-2-(trifiuoromethyl)'-tetrafluoro-1-propanol was 10 grams.

It w-ill be understood that the precedingexamples-have -been givenfor illustrative 'purposes solely and that {this "invention -is 1iot limited' to the specific embodime'iits disclosed therein. n the other hand, it will be readily apparent to those skilled in the art that, subject to the limitations set forth in the general description, the materials, proportions of materials, conditions and techniques employed may be widely varied without departing from the spirit or scope of this invention.

From the foregoing description, it will be apparent that this invention provides a new and improved process for making 1H,lH-2-(trifluoromethyl) -tetrafluoro-l-propanol, which process uses readily available starting materials and produces the desired product in high yields and high purity. 'It is simple and easy to operate and control and can be practiced on a large scale without undue hazards. Therefore, it will be apparent that this invention constitutes a valuable advance in and contribution to the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. The process which comprises reacting about 0.5 mole of hexafluoropropylene with 1 mole formaldehyde and at least 2 moles of hydrogen fluoride at a temperature in the range of from 100 C. to 200 C. and a pressure in the range of from about 600 p.s.i.g. to about 2500 p.s.i.g., there being present not more thm 1 port of water for each part of hydrogen fluoride, and separating from the reaction mass 1H,1H-2-(trifluoromethyl)-tetrafluorol-propanol.

2. The process which comprises reacting about 0.5 mole of hexafluoropropylene with 1 mole formaldehyde and at least 2 moles of anhydrous hydrogen fluoride at a temperature in the range of from 100 C. to 200 C. and a pressure in the range of from about 600 p.s.i.g. to about 2500 p.s.i.g. and separating from the reaction mass 1H, 1H-2-(trifluoromethyl)-tetrafluoro-l-propanol.

3. The process which comprises reacting in the substantial absence of air about 0.5 mole of hexafluoropropylone with 1 mole formaldehyde and from about 4 to about 5 moles of anhydrous hydrogen fluoride at a temperature in the range of from about 125 C. to about 165 C. and a pressure in the range of from about 925 p.s.i.g. to about 2100 p.s.i.g. and separating from the reaction mass 1H, 1H-2-(trifluoromethyl)-tetrafluoro-1-propanol.

4. The process which comprises reacting in the presence of sulfuric acid of from about 96% to 100% concentration about 0.5 mole of hexafluoropropylene with 1 mole formaldehyde and at least 2 moles of anhydrous hydrogen fluoride at a temperature in the range of from 100 C. to 200 C. and a pressure in the range of from about 600 p.s.i.g. to about 2500 p.s.i.g., the concentrated sulfuric acid being present in a proportion of from about 5% to about by weight of the other reactants, and separating from the reaction mass 1H,1H-2-(trifluoromethyl)-tetrafluoro-1-propanol.

5. The process which comprises reacting in the substantial absence of air and in the presence of sulfuric acid of from about 96% to 100% concentration about 0.5 mole of hexafluoropropylene with 1 mole formaldehyde and from about 3 to about 7 moles of anhydrous hydrogen fluoride at a temperature in the range of from about C. to about C. and a pressure in the range of from about 925 p.s.i.g. to about 2100 p.s.i.g., the concentrated sulfuric acid being present in a proportion of from about 20% to about 30% by weight of the other reactants, and separating from the reaction mass lH,1H-2- (trifluoromethyl -tetrafluoro-1-propanol.

6. The process which comprises reacting about 0.5 mole of hexafiuoropropylene with 1 mole formaldehyde and at least 2 moles of anhydrous hydrogen fluoride at a temperature in the range of from 100 C. to 200 C. and a pressure in the range of from about 600 p.s.i.g. to about 2500 p.s.i.g., adding to the reaction mixture at least 20% by weight of sulfuric acid of from about 96% to 100% concentration, and fractionally distilling the mixture to separate the reaction products and recover substantially pure anhydrous 1H,1H-2-(trifluoromethyl)-tetrafluoro-1- propanol.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE PROCESS WHICH COMPRISES REACTING ABOUT 0.5 MOLE OF HEXAFLUOROPROPYLENE WITH 1 MOLE FORMALDEHYDE AND AT LEAST 2 MOLES OF HYDROGEN FLUORIDE AT A TEMPERATURE IN THE RANGE OF FROM 100*C TO 200*C. AND A PRESSURE IN THE RANGE OF FROM BOUT 600 P.S.I.G. TO ABOUT 2500 P.S.I.G., THERE BEING PRESENT NOT MORE THAN 1 PORT OF WATER FOR EACH PART OF HYDROGEN FLUROIDE, AND SEPARATING FROM THE REACTION MASS 1H,1H-2-(TRIFLUOROMETHYL)-TETRAFLUORO1-PROPANOL. 